China's inactivated vaccines have proven to be effective in preventing COVID-19 infection, as well as infection from Delta or other variants, a senior health official said on Tuesday.

Zheng Zhongwei, head of China's COVID-19 vaccine development task force, said at a briefing that the country's inactivated vaccines have been used globally and more than 2 billion doses have been administered across the country.

Data have shown the vaccines, whether used domestically or abroad, are effective in preventing infection, curbing retransmission and significantly reducing serious illness and death, he said.

He also noted that no vaccine is 100 percent effective in protecting against infectious diseases. After vaccination, it is very normal that neutralizing antibody responses decline over time, but the immune memory will persist for a long time.

This means after a full vaccination, the body's immune system will remember the virus and once an infection occurs, the body is still able to quickly produce a large amount of antibodies to remove the virus, reducing risk of re-infection or transmission to other people, as well as the chance of worsening.

Zheng also reaffirmed the public's faith in China's COVID-19 vaccines and urged vaccination be accelerated. "Historical experience in controlling other infectious diseases has taught us vaccines are the effective weapon to defeat viruses," he added.